Semiconductors and other electronic and opto-electronic assemblies are fabricated in groups on a wafer. Known as “dies”, the individual devices are cut from the wafer and are then bonded to a carrier. The dies must be mechanically mounted and electrically connected to a circuit. For this purpose, many types of packaging have been developed, including “flip-chip”, ball grid array (BGA) and leaded grid array (LGA) among other mounting configurations. These configurations typically use a planar printed circuit etched on the substrate with bonding pads and the connections to the die are made by either wire bonding or direct solder connection to the die.
As the overall semiconductor package height is decreased, the thickness of the substrate has likewise been decreased and typical substrates for BGA/LGA packages today are thin film circuits fabricated on KAPTON or other film material, so that the substrates are thin, but with sufficient strength and thermal stability to handle the thermal cycles and handling during the manufacturing process. However, the application of thin films as substrates have led to the need for a stiffener that supports the substrate during the manufacturing process so that the substrate is maintained in proper shape during encapsulation or other final packaging steps.
Typical stiffeners are pre-formed metal strips or rings that are bonded onto the surface of the substrate film after etching/plating of the interconnect circuit patterns and any laminating of multiple substrate layers. Since the stiffeners are added in a separate process after circuit formation, clearances between the stiffener and features of the substrate must be carefully maintained during the bonding process and are generally limited to the periphery of the substrate outside of circuit pattern, wafer bonding, and semiconductor package terminal areas.